Non-specific stimulators (C. parvum and glucan) were employed to enhance the therapeutic response of the L2C leukemia in strain 2 guinea pigs. Administration of glucan or C. parvum 24 hrs post leukemia inoculation demonstrated an 11 and 9 day increase in median survival time respectively. Prophylactically, only C. parvum was effective in contributing to an increase in survival time. Animals receiving specific active immunotherapy of multiple injections of irradiated autologous L2C blast cells following chemotherapy were refractory to a viable cell challenge while displaying a corresponding increase in CMI in vitro. Animals treated with chemotherapy alone succumbed to a similar challenge. Treatment of the leukemia followed chemotherapy with adoptively transferred syngeneic or allogeneic spleen cells specifically sensitized to L2C was also successful. Animals receiving syngeneic cells have survived significantly longer than either drug controls or recipients of allogenic cells and are presently still alive. The biological characteristics of a new strain 2 guinea pig stem cell leukemia is described in addition to its growth characteristics and immunogenicity. Employing a spontaneous rat mammary carcinoma, an indirect relationship has been observed between concomitant immunity and metastases.